The invention relates to a voltage-controlled oscillator (VCO) circuit including an oscillator circuit connected to a voltage source furnishing a substantially constant supply voltage, and comprising at least one varactor, and a control voltage generator circuit whose output is connected to the anode of the varactor, the frequency of the oscillation signal of the oscillator circuit being variable by changing the control voltage.
Voltage-controlled oscillator circuits, configured integrated as a rulexe2x80x94as used for example in phase-locked loopsxe2x80x94are known in prior art. They are often powered by fixedly predefined battery voltages. Since the trend in electronics is to continually reduce standard battery voltages this poses a problem in such circuitry by the reduction in the supply voltage making it increasingly more difficult to achieve an adequate tuning range of the varactor and thus the frequency range of the oscillation signal.
Another possibility of achieving the oscillator circuitry would be to completely change the circuit configuration by grounding the anode of the varactor. However, this would necessitate additional circuit modules such as blocking capacitors and resistors, which in turn diminish the tuning range and on top of this, would have a negative effect on the phase noise and current consumption.
An objective of the present invention is thus to provide a voltage-controlled oscillator circuit which even in conjunction with small, substantially constant, supply voltages, as furnished by batteries, can still be put to use whilst achieving low phase noise, low current consumption and a wide tuning range.
This objective is satisfied by the voltage-controlled oscillator circuit as cited at the outset in which a voltage converter circuit and an ON/OFF switch therefor is located between the voltage source and the oscillator circuit, the conversion factor of the voltage converter circuit being selected so that a wide tuning range of the varactor and thus a wide frequency range of the oscillation signal is available.
The invention features several advantages. Thus, the complete configuration of a voltage-controlled oscillator circuit as used hitherto can continue to be used, more particularly enabling the control voltage generator circuit to be taken over with no change, i.e. only additional components needing to be added without requiring any change to already existing components. Since good filtering of the signal of the voltage converter circuit is permitted, any increase in phase noise is avoided. Due to relatively high (blocking) voltages always existing across the varactor when using the voltage converter circuit, any noise and hum existing has only a minor effect on the output signal of the oscillator circuit. In addition, the voltage-controlled oscillator can continue to be powered by a defined supply voltage. There is no need to change components or to use several voltage sources.
Unlike other oscillator circuit assemblies in which the anode of the varactor is grounded via resistors, the control range of the proposed oscillator circuit is not diminished by additional blocking capacitors. This enables the frequency range of the circuit to be significantly increased by simple and effect means for the oscillator circuit in accordance with the invention unlike such prior art circuitry.